The GCL team is happy to announce the release of version 2.6.5, the latest achievement in the 'stable' series. This release is a minor modification to version 2.6.4. From the changelog:

As an example of the recent performance enhancements in GCL, Matt Kaufmann, one of the ACL2 co-authors, reports significantly improved timings for the ACL2 regression suite. When ACL2 2.8 was released, GCL was in pre-release mode for 2.6.2, and provided the following regression suite timings as reported on http://www.cs.utexas.edu/users/moore/acl2/v2-8/installation.html: Since version 2.6.3, a reasonably comparable calculation on the same machine takes about 7800 user seconds (on a slightly updated ACL2). For the latest information, capabilities, and status of GCL stable, please see the 2.6.2 release notes here